From the past, a light emitting device for spot illumination that illuminates a specific region by radiating light in a specific direction is used for usage such as auxiliary illumination, ceiling illumination, or illumination for a showcase. Further, in recent years, a light emitting diode (LED) is used as a light source of a light emitting device for spot illumination.
The light emitting diode has characteristic features such as having a small scale and emitting light of a vivid color with a good electric power efficiency, having no fear of filament breakage in a bulb because of being a semiconductor element, being excellent in initial driving characteristics, and being strong against vibration or repetition of on-off energization.
A plane light source device (illumination device) for a display device having such a light emitting diode as a light source is known (for example, Patent Literature 1). Patent Literature 1 discloses an illumination device including a light emitting diode and an illumination lens having a cylindrical shape that controls the distribution of light emitted from the light emitting diode. FIG. 1 is a cross-sectional view of illumination device 1 including illumination lens 2 having a cylindrical shape disclosed in Patent Literature 1.
Also, illumination equipment that controls the distribution of light emitted from a light emitting diode by using an illumination lens having a symmetric shape with respect to the optical axis of the light emitting diode is known (for example, Patent Literature 2). The illumination lenses described in Patent Literature 1 and Patent Literature 2 each can condense and emit the light emitted from a light source so that the light having a sufficient light quantity may be delivered to a site of the illuminated surface located away from the light source.